Deposition and characterization of few-nanometers-thick superconducting Mo-Re films

We report on the fabrication and investigation of few-nanometers-thick superconducting molybdenum–rhenium (Mo–Re) films intended for use in nanowire single-photon superconducting detectors (SSPDs). Mo–Re films were deposited on sapphire substrates by DC magnetron sputtering of an Mo(60)–Re(40) alloy target in an atmosphere of argon. The films 2–10 nm thick had critical temperatures (Tc) from 5.6 to 9.7 K. HRTEM (high-resolution transmission electron microscopy) analysis showed that the films had a homogeneous structure. XPS (x-ray photoelectron spectroscopy) analysis showed the Mo to Re atom ratio to be 0.575/0.425, oxygen concentration to be 10%, and concentration of other elements to be 1%.